Measuring system



Patented Nov. 5, 1946 MEASURING SYSTEM John P. Smith, Cranbury, N. 1.,asslgnor to Radio Corporation of America, a corporation of DelawareApplication July 25, 1944, Serial N0. 546,543

Claims.

This invention relates to measuring systems such as are suitable for themeasurement of the time interval required for an object to traverse thedistance between two points or the like. It has for its principal objectthe provision of an improved system and method of operation whereby timeis measured in terms of electrical charges which may be counted orrecorded at a rate much slower than that at which they were established,thus permitting very short intervals of time to, be computed bymechanical counters or other slowly acting devices.

The invention includes, among other things, a cathode ray tube (such asthat disclosed by a copending application of Iams et al. Ser No. 492,-

== 658, filed June 26, 1943) which is provided with a multi-elementelectrode on which electrical charges are stored transversely inresponse to the positive half cycles of high frequency impulses appliedto the control grid of the tube. Associated with the cathode ray tubeare means for starting and stopping the application of high frequencyimpulses to its grid in response to different positions of the objectunder observation, and for simultaneously controlling movement of thecathode ray or electron beam along the multielement electrode of thetube. The resulting electrical charges are stored at a relatively rapidrate under conditions such that secondary electron emission from themulti-element electrode,

.frequency cycles passed by the control grid of the tube to itsmulti-element electrode. When this number is known, the time requiredfor the object to travel between predetermined observation points isreadily ascertained.

The measuring system of this invention ha uses other than that ofmeasuring the time required for an object to traverse the distancebetween predetermined points. For example, it is adapted to themeasurement of any quantity susceptible of being represented by a seriesof electrical charges distributed transversely of the multi-elementelectrode or the equivalent,

Important objects of the invention are the provision of an improvedtime-measuring system which utilizes counters of well-known types; theprovision of an improved system for measuring the speed of projectilesand the like; and the provision of means for measuring, in term ofsuccessively established electrical charges, any quantity susceptible ofbeing represented by such charges.

The invention will be better understood from the following descriptionconsidered in connection with the accompanying drawings, and its scopeis indicated by the appended claims.

Referring to the drawings:

Figure 1 is a wiring diagram of a. measuring system embodying theinvention in a form suitable for measuring the instantaneous velocity ofan object,

Figure 2 is a similar diagram of a modification adapted to measure thevelocity of an object at diflferent points in its path of travel,

Figure 3 is an explanatory diagram showing a type of record produced bythe apparatus of Fig. 2,

Figures 4, 5 and 6 illustrate systems similar to those of Figs. 1 and 2,with the exception that the cathode ray or commutator tube is providedwith only one electron gun and has associated with it means forutilizing this gun both to put on and take off the charges of themulti-element electrode,

Figure 7 is a wiring diagram of a phase inverter and clipper circuitwhich is interposed between the pick-up coils and the trigger tube ofthe system shown by Fig. 4, and

' Figure 8 illustrates a trigger tube. which may be used to start andstop the application of high frequency impulses to the multi-element ofthe commutator tube.

The system of Fig. 1 includes a storage or commutator tube ID which hasa'pair of electron guns I2l3-I4 and [5-46-11 arranged to form separateelectron beams which are spaced from one another within the tube.Potentials for operating these guns are derived from a suitable sourcethrough voltage dividers and [9. A mounting plate and shield 20,provided with an apertured flange 2|, is positioned between the pathsfollowed by the electron beams formed by the guns l2l3l4 and i5-|6.l|.

The multi-element or composite target of the tube ll includes aplurality of conductors 22, accurately spaced from one another andclamped between mica" plates which are held against the wires by a metalplate 23 and a metal signal output plate 21. There may be, for example,400 such wires parallel with one another in the same plane, each oneinch long, and protruding at opposite ends from between the plates by adistance of 5 inch, to form a sort of double-edged comb.

made to have any desired relation.

The point of contact between the beams and the target is along the edgesof this comb. Otherwise stated. the beam of the gun |2--|3|4 movesacross the upper ends of the wires 22 and the beam of the gun |5--|6||moves across the lower ends of the wires 22.

The beam of the gun |2-|3--|4 passes to the target through one aperturein the shield 2|, be-

' tween deflectors 25-25, between shield 20 and a centering deflector21, and between secondary electron collectors 28 and 29. The beam 01 thegun |5|5-|| passes to the target through a diflerent aperture of theshield 2|, between deflectors 30 and 3|, between the shield 20 and acentering .deflector 32, and between secondary electron collectors 33and 34. The beam of the gun |5|5|| is utilized to establish electricalcharges linearly across the lower ends of the wires 22 and the beam ofthe gun |2--|3-|4 is utilized to remove these charges. The rates atwhich these charges are established and removed are obviously dependenton the voltages applied t. the deflectors 30-3| and 25-26 and may be Inthe illustrated embodiment of the invention, the electrical charges areestablished on the lower ends of the wires 22 at a very rapid rate andare removed at a much slower rate.

To this end, the anode voltage of gun |5-|5 I1 is adjusted for asecondary electron emission of less than unity, while the anode voltageof the gun |2|3|4 is adjusted for a secondary electron emission of morethan unity. Under these conditions, negative electrical charges areestablished across the conductors 22, in response to the positive halfcycles of impulses delivered from a l-k. 0. generator 35 through atriode 36 and a transformer 31 to the control grid of the gun |-|6|'|.These charges are removed from the upper ends of the wires 22 inresponse to high frequency impulses supplied from a 460-k. 0. impulsegenerator 33. The output of the tube Ill delivered at the target plate24 is a 460-k. c. signal, which is modulated by the charges on the wires22 at a rate determined by the speed at which the beam of the gun|2|3-|4 is deflected. This speed of deflection is determined by the rateat which the potential between the deflectors 25-25 is changed.

Since the high frequency impulses of the oscillator 35 are applied tothe control electrode l5 of the cathode ray tube I0 only during the timeinterval between the occurrence of two events,'

such as the passage of the bullet 39 between the coils 40 and 4|, itfollows that there are established across or transversely of themulti-element electrode of the tube ill a series of separate electricalcharges which (1) are representative of the positive half cycles of theimpulses delivered by the oscillator 35, and (2) continue to beestablished only so long as the bullet 39 is between the coils 40 and4|. The charges thus established vary in magnitude from conductor toconductor of the electrode, reaching the highest value when theinstantaneous voltage of the positive half cycle is a maximum. Duringthe removal of these charges, they modulate impulses delivered from ahigh frequency oscillator 33 and are thereafter detected and counted orrecorded. I

The electrical charges at the lower ends of the wires 22 are establishedduring a time interval which is determined by the travel of.a projectilebetween a pair of pickup coils 40 and 4|.

It will be noted that the coil 40 is coupled to one grid 42 of amultivibrator unit through triodes 43 and 44, and that the coil 4| iscoupled to another grid 45 of the multivibrator through triodes 45 and41. With these connections, a positive pulse is applied to the grid 42in response to passage of the projectile 39 through the coil 49.Similarly a positive pulse is applied to the grid 45 when the projectile39 passes through the coil 4|.

The multivibrator unit is of a well-known type which includes anoderesistors 48 and 49, triodes 50 and 5| and grid resistors 52, eachinterposed between the anode of one triode and the grid of the othertriode. In the operation of such a multivibrator or trigger unit, onlyone of the triodes conducts current at a time and current is transferredfrom one triode to the other in response to the application of apositive pulse to the grid of the triode which is not conducting. Thus,if the triode 50 is conducting and a positive pulse is applied to thegrid 4|] of the triode 5|, current is transferred from the triode 50 tothe triode 5|, and vice versa.

The potential drops of the resistors 48 and 49 are utilized to controlthe connection between the generator 35 and the grid of the gun |5-|5-They also control the connection between the deflectors 3||3| and thepentodes 53 and 54, through which deflecting potential is applied from acapacitor 55 connected to the anode of the triode 5|. Potential is alsoapplied from the anode of the triode 5| to the grid of the gun |5- |5-||for blanking its beam. A reset switch 55 is provided for establishing astandby condition with current in the triode 50 of the trigger unit,

With current in the triode 50, passage of an object through the coil 40produces at the grid 42 a positive impulse whereby current istransferred to the triode 5| and a more negative voltage (due to thepotential drop of the resistor 49) is applied to the capacitor 55 and tothe cathode of the gun |5-|5--||, thereby unblanking the beam of thisgun and operating through the pentodes 53 and 54 to start movement ofthe beam across the lower ends of the wires 22. At the same time, a morepositive potential is applied to the grid of the triode 35, therebypassing high frequency impulses from the generator 35 to the controlgrid of the gun |5-|6-|'| and producing on the lower ends of the wires22 an electrical charge for each cycle of these impulses. Due

to the movement of the beam, these charges are arranged in linearrelationship with one another. When the object 39 passes through thecoil 4|,

a positive pulse is applied to the grid 45 of the triode 50, current istransferred from the triode 5| to the triode 50 of the trigger unit, thebeam of the gun |5-|6-|'| is blanked out, the supply of high frequencyoscillations through the triode 35 to the grid of the gun |5-|5-|| isinterrupted, and the deflectors 303| have their potentials changed to avalue adapted to re-establish the beam in its original startingposition.

The time required for the object 39 to traverse the distance between thecoils 39 and 4| is readily determined by counting the number of 10-k. c.cycles passed while the object is between the coils. These cycles,represented by electrical charges linearly disposed on the wires 22, arecounted at a much lower rate than they are produced.

These linearly disposed electrical charges are removed from the wires22, one after another, in response to movement of the electron beam ofthe gun |2-|3--|4 and are registered in a counter 5! which is coupled tothe output plate 24 through a transformer 58, a pentode 59, second andthird intermediate frequency amplifiers 58 and 8|, a detector 62 and anamplitude limiter 88. As previously indicated, there is deliveredfromthe output plate 24 a 460-k. c. signal which is derived from thegenerator 38 and is modulated at a frequency determined by the speed atwhich the electrical charges are removed from the wires 22.

Removal of the charges from the wires 22 is effected under conditionssuch that (1) secondary electron emission is greater than unity and (2)the beam is moved across the upper ends of the wires 22 at a speeddetermined by the speed of a motor 58. This motor is controlled througha switch 59 and functions through a speed reduction gear 6|) to rotate asingle segment commutator 8| and potentiometers 62 and 63. Rotation ofthe contact members of the potentiometers 52 and G3 gradually varies thepotential between the deflectors and 26, so that the beam is movedacross the upper ends of the wires 22. Rotation of the commutator 8|serves to interrupt the circuit of the motor 58 at the end of eachrevolution, thus completing the cycle of operation.

The system of Fig. 2 is similar to that of Fig. 1 in many respects, butdifiers therefrom in that it is adapted to measure change in thevelocityof an object as it moves between successive points. As illustrated inFig. 2, it produces a record such as that shown by Fig. 3, wherein themoving object 39 is shown at successive points in its travel and itschange in velocity as it passes from point to point is indicated.

In Figs. 1 and 2, similar parts are indicated by the same referencenumerals. I'hus, the coils 48 and 4| of Fig. 2 function in the samemanner as the similarly designated coils of Fig. 1 and other partscommon to the two figures function as explained in connectionwith Fig.1.

Interposed between the coils 48 and 4| of Fig. 2 are additional coils 64to 81, which are connected to the grid of the gun |5|6|1, respectively,through trigger units 68 to II. Passage of the object 38 through thecoils 61, 88, 55 and 64 in each case trips the corresponding triggercircuit 1|, 18, 88 or 58 and produces a marker pulse 12 (see Fig. 3),which is applied to the grid of the gun '|5|8-|1 together with the 10-k.c. impulses supplied from the oscillator 35. The amplitudes of themarker pulses are made greater than those of the 10-k. c. pulses 13,50that the markerpulses 12 print blacker on the facsimile recorder 14, towhich the output plate 24 is connected through-an amplifier, asindicated in Fig. 2. Knowing the distance between the coils or markerpu1ses,'the velocity of the object at difshown in Fig. 7), whichcontrols the supply of l0-k. c. impulses from the generator 11 through aswitch 18 to the grid |5 of the tube Ill.

The output of the put on pickup coil 48 is also supplied to a trig ertube 19 which is the same as the tube 18 and functions through a sourceof deflecting current 88 and a switch 8| to energize the deflectingcoils 30' and 3|, when the object 39 passes through the first pickupcoil 48. For returning the beam to its starting or standby position, areset switch 82 is provided for applying a negative pulse to the triggertub 19 as hereinafter explained.

From the foregoing explanation, it is evident that the system of Fig. 4operates to establish charges on the wires 22 in the same manner as thesystems of Figs. 1 and 2. The taking off and counting of these chargesby the counter 51 involves certain switching operations which areperformed by the parts shown at the lower lefthand corner of Fig. 4.

These parts include a plurality of double throw switches 83, 84, 18 and8|. The switch 83 connects the first anode Hi to a 400 volt lead in itslower position and to a +100 volt lead in its upper position. The switch84 connects the cathode of the tube iii to a -500-volt lead in its lowerposition and to ground in its upper position. The switch 18 connects thegrid |5 to the trigger tube 18 in its lower position and to a 15 voltlead in its upper position. The switch 8| connects the deflecting coils38? and 3| to the source 88 in its lower position and to a potentiometer85 in its upper position.

The potentiometer 85 may be of atype similar to the potentiometer 62 and63 of Fig. 1. Its contact arm is moved by the motor 58, which is coupledto the potentiometer through the gear 58 and is supplied with powerthrough the control switch 59. The switch 59 also controls the supply ofoperating-current to the potentiometer 85 and to a put on and take off"relay 86, by whichthe switches 83, 84, 18 and 8| are movedsimultaneously to their upper or "take off positions.

With the switches in their "take of! positions, the potentiometer isrotated to vary the current of the coils 3|) and 3| by which the beam ismoved across the ends of the wires 22 and their charges are removed at arelatively low rate and counted by the counter 51, as previouslydeferent points in its travel is readily determined.

Such data is useful forplotting curves of velocity versus distance andthe like.

In the system of Fig. 4, the storage tube l8 (shown more or lessdiagrammatically) is the same as that of Figs. 1 and 2, with theexception that (1) it includes only one electron gun, (2) the deflectors30 and 3| are replaced by deflecting coils 38' and 3| and (3) it hasassociated with it such relay and switching means as are required forutilizing the single beam of the tube both for putting on and taking 011the charges of the wires 22.

this modification of the invention, the outpu'tsf o'f, the pickup coils48 and-4| are supplied through aphase inverter and clipper 15 (detailsshown'in Fig. 6) to a trigger tube 18 (details scribed in connectionwith Figs. 1 and 2.

The system of Fig. 5 is similar in some respects to that of Fig. 4 andin other-respects to that of Fig. 2. It includes a plurality ofpickupcoils 81 to 94 which are suitably spaced between the coils 40 and4|. when the object 39 passes through the coil 48, the beam of the tubel8 starts tomove. During this movement, a positive pulse is appliedthrough a mixer 95 to the grid i5 each time the object 38 passes throughone of the coils 81 to 94. The resulting charges on the conductors 22are removed as in the system of Fig. 4 and are registered by therecorder 14. The beam is returned to its standby position in response tooperation of the reset switch 82.

The system of Fig. 6 diflers from that of Fig. 5 in that the pickupcoils are arranged in pairs, one for each section under measurement. Thestarting pulse for the trigger tube 18 is positive and its stoppingpulse is negative. The trigger tube starts deflection in response to thefirst positive pulse, but is unaffected by the negative pulses whichoccur when the object passes through the second coil of each pair. Thereare 7 thus produced on the wires 22 group of charges, one for each pairof coils. The charge "take of! procedure is the same as that previouslydescribed. This system functions with somewhat greater accuracy thanthat of Fig. 5, but requires more apparatus.

Fig. 7 is a wiring diagram of a phase inverter and clipper, such as thatillustrated by the box 15. and Fig. 8 is a wiring diagram of a triggertube, such as that illustrated in Fig. 4 by the boxes II and II.

As indicated by Fig. 7, the output from the pickup coil 40 istransmitted through a channel including triodes DI and 81, to produce atan output lead 08 a pulse of positive polarity. This is utilized. aspreviously explained, to initiate movement of-the beam of the tube Illand to start the application of highfrequency impulses to its controlgrid. To this end, the positive pulse is applied to an electrode I of atube 99 (see Fig. 8) which permits the passage of 10-11. c. impulsesfrom the generator 11 of Fig. 4 through the switch II to the grid II,for example. This application of high frequency impulses to the grid llcontinues until a negative pulse is applied to the electrode I" throughthe lead iii, in response to passage of the object through the coil II.The output of the coil H is transmitted to the lead HII through achannel which includes the triode I02 (see Fig. 7).

The tube 99 is of the secondary electron emission, electron multipliertype. It functions to start or stop the application of high frequencyimpulses to grid of the tube ID in about one microsecond. A morecomplete description of it is to be found in the Bell LaboratoriesRecord for April, 1943, at page 233.

It is apparent that the multivibrator 50- of Fig. l and the tube ll ofFig. 4 perform the same functions and may be interchanged with oneanother without aifecting 'the result produced. Other rearrangements ofthe parts of the various figures may likewise be made withoutsurrendering the advantages of the present invention.

I claim as my invention:

1. The combination of means for forming an electron beam, means forsubjecting said beam to high frequency impulses, a plurality ofconductive elements electrically insulated from one another, and meansresponsive to control impulses separated by predetermined time intervalsfor operating said beam to establish on said elements electrical chargeswhich are separately positioned to represent instantaneous values ofsuccessive half-cycles of said high frequency impulses, and meansincluding said beam-forming means for dissipating said charges at a ratewhich is low with respect to the rate at which said high frequencyimpulses follow one another.

2. The combination of means for forming an electron beam, means forsubjecting said beam to high frequency impulses, a plurality ofconductive elements electrically insulated from one another, meansresponsive to control impulses separated by predetermined time intervalsfor operating said beam to establish on said elements electrical chargeswhich are separately positionea to represent instantaneous values ofsuccessive half-cycles of said high frequency impulses, and meansseparate from said beamforming means for dissipating said charges at arate which is low with respect to the rate at which said high frequencyimpulses follow one another.

3. Thecombination of means for forming an electron beam, a plurality ofelements spaced from one another, means for supplying high fre quencyimpulses, means for producing electrical effects separated by apredetermined time interval, means responsive to the first of saideffects for operating said beam to establish on said elements electricalcharges which are representative of successive cycles of said highfrequency impulses and responsive to the last of said effects foroperating said beam to terminate the establishment of said charges.

4. The combination of means for forming an electron beam, a plurality ofelements spaced from one another, means for supplying high frequencyimpulses, means for producin electrical effects separated by a timeinterval, means responsive to the first of said effects for operatingsaid beam to establish on said elements electrical charges which arerepresentative of successive cycles of said high frequency impulses andresponsive to the last of said effects for suppressing said beam toterminate the establishment of said charges, and means including saidbeam-forming means for counting said charges.

5. The combination of means for forming an electron beam, a plurality ofelements spaced from one another, means for supplying high frequencyimpulses, means for producing electrical effects separated by a timeinterval, means responsive to the first of said effects for operatingsaid beam to establish on said elements electrical charges which arerepresentative of successive cycles of said high frequency impulses andresponsive to the last of said effects for suppressing said beam toterminate the establishment of said charges, and means separate fromsaid beam-forming means for counting said charges at a rate which isslow with respect to that at which they were established.

6. The combination of means for forming an electron beam, a plurality ofelements spaced from one another, means for supplying high frequencyimpulses, means for producing electrical effects separated by a timeinterval, means responsive to the first of said effects for operatingsaid beam to establish on said elements electrical charges which arerepresentative of successive cycles of said high frequency impulses andresponsive to the last of said effects for suppressing said beam toterminate the establishment of said charges, and means responsive toeffects intermediate said first and last effects for separating saidcharges into groups representative of the time intervals between saidintermediate effects.

7. In a device for transmitting high frequency impulses only between theoccurrence of two events, the combination of means for forming anelectron beam, a plurality of conductive elements electrically insulatedfrom one another, and means responsive to the occurrence of one of saidevents for operating said beam to establish on said elements one afteranother electrical charges representative of the instantaneous voltageof the positive half-cycles of said impulses and in response to theoccurrence of the other of said events for terminating the establishingof said charges.

8. In a device for transmitting high frequency impulses only between theoccurrence of two events, the combination of means for forming anelectron beam, a plurality of conductive elements electrically insulatedfrom one another, means responsive to the occurrence of one of saidevents for operating said beam to establish on said elements one afteranother electrical charges representative oi the instantaneous voltageoi. the positive half-cycles of said impulses and in response to theoccurrence of the other of said events for terminating the establishingof said charges, and means for removing said charges one after anotherat times separated by time intervals which diiler in length from thetime intervals between the establishment of said charges.

9. The combination of means for producing separate electrical charges atconstant frequency, means for starting and stopping the production ofsaid charges in response to the occurrence of events occurring atdifi'erent times, and means for counting said charges one after anotherat a frequency which is lower than said constant frequency.

currence of the other of said events.

JOHN P. SMIITH.

